Electrical connection between two faces of a substrate and manufacturing process

ABSTRACT

Electrical connection between two faces of a substrate and manufacturing process. 
     The connection is made by a part ( 46 ) of a conducting or semi conducting substrate ( 20 ) completely surrounded by at least one electrically insulating trench ( 32, 36, 44 ). A contact pad ( 42 ) is located on the back face ( 40 ) and conducting tracks ( 38 ) are located on the front face. The connection is made through the substrate itself. 
     Application to the manufacture of circuits, components, sensors, etc.

DESCRIPTION

1. Technical Field

The purpose of this invention is an electrical connection between twofaces of a substrate and a process for making this connection. Itsapplications include the manufacture of electronic components orcircuits or devices necessitating electrical connections like magneticheads or sensors.

2. State of Prior Art

Document FR-A-2 637 161 describes a process for making electricalconnections through a substrate. This process is illustrated in FIGS.1A, 1B and 1C attached. An insulating layer 12 is deposited on asubstrate 10 and the back face of the substrate is scanned at a definedpitch by a laser beam with an appropriate wavelength. The laserradiation is absorbed by the substrate and causes local abrasion of thesubstrate. When the entire thickness of the substrate has been abraded,radiation reaches the insulating layer 12 which is transparent to thechosen radiation. It remains intact and therefore forms a bottom forholes perforated in the substrate and which are consequently not throughholes. Thermal oxidation is then carried out, particularly creating aninsulating layer 14 on the wall of holes and on the back face of thesubstrate (FIG. 1A).

A conducting layer 16 is then deposited that coats the sides and thebottom of the holes. An etching technique is then used to remove part ofthe insulating layer 12 covering the front face of the conducting layerto create an opening 18 (FIG. 1B).

An electrical contact is then made on the metallic layer 16 through aconducting pad 18 (FIG. 1C). The electrical connection between the frontface and the back face of the substrate is then made through themetallic material of the pad 18 and the metallic layer 16. The next stepis to use traditional means to make the electrical circuit on the frontface of the substrate.

This type of process has at least two disadvantages:

due to the presence of holes in the substrate, particular precautionshave to be taken during some operations related to manufacturing of thecircuit, such as spreading of resin, cleaning of parts, etc.;

the presence of a metallic material in the holes different from thesubstrate creates stresses and deformations during steps in whichtemperatures higher than the ambient temperature are necessary; thesesame stresses and deformations are very harmful during operation of thecomponent at high temperature.

The purpose of this invention is to overcome these disadvantages, byavoiding the presence of holes and reducing differences in naturebetween different materials.

Document EP-0 926 726 describes a process for making an electroniccircuit in which a trench is perforated in a stack formed from a semiconducting substrate, an insulating layer and a dielectric layer. Thistrench is filled with an oxide. The next step is to drill an openingthat is filled with metal. The metallic cylinder makes the connection,as in a normal technique rather than a stack of layers, since the stackof layers comprises two insulating layers.

The abstract for Japanese patent vol. 1995, No. 02, Mar. 31, 1995 (andJP 06 310 489) describes an etching process for a semi conductingsubstrate. The objective is not to create a permanent connection but tosimplify an electrolytic process by enabling the lower face of asubstrate immersed in an electrolyte to be raised to an appropriatepotential.

The abstract for Japanese patent, vol. 009, No. 251 (E-348), Oct. 8,1985 (and JP 60 10 1945) describes a process for making a semiconducting component in a substrate and for isolating this componentfrom the rest of the substrate. Therefore, the objective is not to makea connection between one face of the substrate and the other face.

Document EP-A-0 974 817 describes a circuit card for a detector,comprising a cylindrical insulating region formed throughout thethickness of the substrate, the insulation flush with the surface of thesubstrate.

PRESENTATION OF THE INVENTION

The invention proposes an electrical connection (called “via” conductor)in which the substrate is a conductor (or semiconductor), thisconducting property being used to make the connection. It will beobserved that in prior art that has been described, if a conductingsubstrate is used, this conductivity will not always be advantageoussince the connection would always be made through an add-on material(layer 16) that is different from the substrate.

According to the invention, the substrate itself will be used as anelectrical connection means between the two faces. The part of thesubstrate that makes this connection must naturally be electricallyinsulated from the rest of the substrate. This insulation function isdone by at least one trench (that can also be called a partition orwall), extending throughout the thickness of the substrate andcompletely surrounding part of the substrate forming the connection.This (or these) trench(es) must be at least partly filled in to achievemechanical strength of the entire substrate.

Specifically, the purpose of this invention is a process for making anelectrical connection between two faces of a substrate comprising thefollowing operations:

the starting point is a conducting or semi conducting substrate,

at least one electrically insulating trench completely surrounding partof the substrate is made throughout the thickness of the substrate, thistrench being filled in over at least part of its depth,

a first conducting means is deposited on one of the faces of thesubstrate, this means being in electrical contact with the substrateover the part completely surrounded by the trench,

this process being characterized in that:

a first groove is formed starting from a first face of the substrate,and this first groove is filled in by at least one insulating material,

the substrate is thinned until it has the required thickness,

a second conducting means is formed on the thinning face of the thinnedsubstrate facing the part of the substrate that is completely surroundedby the groove,

a second groove is formed starting from the thinning face of the thinnedsubstrate, facing the first groove and opening up onto the materialfilling the first groove,

said electrical connection thus being set up by said part of thesubstrate completely surrounded by the trench and by the first andsecond conducting means.

Another purpose of this invention is an electrical connection obtainedby the process defined above. This connection comprises:

at least one electrically insulating trench extending throughout thethickness of the substrate and completely surrounding part of thesubstrate, this trench being filled in over at least part of its depth,

a first conducting means on one of the faces of the substrate, thismeans being in electrical contact with the substrate in the partcompletely surrounded by the trench,

a second conducting means on the other face of the substrate, inelectrical contact with the substrate in said part completely surroundedby the trench,

said connection thus being set up by said part of the substratecompletely surrounded by the trench and by the first and secondconducting means,

this electrical connection being characterized in that:

the filled in part of the trench comprises a first groove formed in thesubstrate starting from a first face of the substrate, an electricallyinsulating material filling in this first groove and a second grooveformed in the substrate, starting from a second face of the substrate,this second groove having a bottom opening up into the filled in part ofthe trench.

The trench may be formed from two grooves facing each other and eachformed from the opposite sides of the substrate. One of the grooves, orpossibly both, are filled in.

According to one embodiment, the filled in part of the trench comprisesa first groove etched in the substrate starting from a first face of thesubstrate, an electrically insulating material filling in this firstgroove.

According to another embodiment, the wall of the first groove is coveredby an insulating layer and the groove is filled in by another material.This other material may be electrically conducting or semi-conducting;preferably, the coefficient of expansion of this material is similar tothe coefficient of expansion of the substrate.

This trench can be made by etching two communicating grooves startingfrom the two faces of the substrate and filling in at least one of themor making a single groove and thinning the other face of the substrateas far as the said groove.

It is also possible to make several concentric or non-concentrictrenches, for example two, one on the inside and one on the outside.

In the above definitions, the “first” and “second” faces may be the“front” and “back” faces of the substrate or the “back” and “front”faces, since these names are conventional and have no limitative nature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C described above illustrate a process for making aconnection according to prior art;

FIGS. 2A and 2B illustrate a top view and a sectional view of a firststep in a process according to the invention;

FIG. 3 illustrates formation of a first groove;

FIG. 4 illustrates a variant in which this first groove is filled in byan insulating material;

FIG. 5 illustrates another variant in which the wall of the first grooveis covered with an insulating layer;

FIG. 6 illustrates the groove thus covered being filled in;

FIG. 7 illustrates an additional step in the formation of layers to formcircuits or interconnections on the front face of the substrate;

FIG. 8 illustrates an operation to thin the substrate through the backface;

FIG. 9 illustrates the formation of a contact pad on the back face ofthe substrate;

FIG. 10 illustrates the formation of a second groove in the thinnedsubstrate, and shows the completed electrical connection in anembodiment in which the second groove is not filled in;

FIG. 11 illustrates another variant in which the two grooves are filledin by insulating materials;

FIGS. 12A, 12B, 12C show various trench patterns and illustrate avariant with two triangular grooves.

DESCRIPTION OF PARTICULAR EMBODIMENTS

FIGS. 2A and 2B show a substrate 20, for example in the form of a 500 μmthick silicon slice with a resistivity of 2 mΩxcm. This substrate has afirst face 21 that will be denoted the “front” face and a second face 22that will be denoted the “back” face. The front face 21 is covered witha photosensitive resin 24 that is insolated through a mask to define aclosed pattern that will correspond to the future trench. In theembodiment shown, this closed pattern is a circular ring 26, for whichthe inside diameter may for example be 180 μm and the width may be 6 μm.When the resin is developed, the front face 21 of the substrate isexposed along the ring 26.

The substrate is etched, for example by dry etching, in the exposed areato obtain a groove 28 as illustrated in FIG. 3. For example, the depthof this groove may be 60 μm.

After removal of the resin, this groove may be filled in with aninsulating material reference 30, in a first variant illustrated in FIG.4.

In another variant illustrated in FIG. 5, the entire substrate isoxidized by heat such that a thin insulating layer 32 (in fact a layerof silica if the substrate is made of silicon) covers the inside wall ofthe groove. An insulating layer 33 is also deposited on the back face.The next step is to deposit a material preferably with a coefficient ofthermal expansion similar to that of the substrate, for example usingchemical vapor deposition (CVD). For example, it could bepolycrystalline silicon if the substrate is made of silicon. Thismaterial is denoted reference 36 in FIG. 6. A layer 37 may also bedeposited on the back face. The next step is to polish the front face,for example using a mechanical-chemical process to leave material 36only in the grooves.

FIG. 7 illustrates a next step in which a first conducting means 38 ismade which, in the variant illustrated, is in the form of variousconducting tracks on the front face of the substrate. This may beobtained by known processes in micro-electronics. These tracks are inelectrical contact with the substrate in the area located inside thefirst groove. A protective layer 39 may cover the complete assembly.

The substrate can then be thinned as shown in FIG. 8, for example by amechanical, mechanical-chemical or chemical process until the requiredthickness, for example 250 μm, is obtained. The new back face is denotedreference 40. FIG. 9 shows a second conducting means 42, for example acontact pad made for example of metal, on this back face. Metallic wirescould be soldered onto this pad, or weld beads could be deposited(depending on the application). The location of the second conductingmeans 42 corresponds to the inside of the ring defined by the firstgroove made on the front face.

As illustrated in FIG. 10, the next step is to form a second groove 44starting from the back face 40, using the same photolithography andetching processes as for the first groove. Etching is continued until itreaches the infill material in the first groove. The part 46 of thesubstrate is thus completely isolated. This part 46 forms an electricalconnection electrically connecting the first conducting means 38 made onthe front face and the second conducting means 42 on the back face.

In the example taken, with the dimensions given and using a siliconsubstrate, a connection is obtained with a resistance of the order of 1Ohm. Obviously, this is simply an example and in no way limits theinvention. Another value can be obtained by modifying the thickness ofthe substrate and/or the inside diameter of the ring, and/or theresistivity of the substrate.

FIG. 11 illustrates another embodiment in which the first groove formedon the front face is filled in by an insulating material 48 (for exampleglass, silica, etc.), the second groove formed on the back face can alsobe filled in by an insulating material 50 (glass, silica, etc.).

According to another embodiment, the trench only comprises one filled ingroove, the substrate then being thinned until the groove infillmaterial is exposed.

The last step shown in FIGS. 12A, 12B and 12C is three closed profiles60 that are not circular, namely square, triangular and hexagonalprofiles respectively. All of these shapes are simply given as examples.FIG. 12B shows the case in which two trenches 61 and 62 are made. Itwould be possible to make more, regardless of the shape of the profile.

Furthermore, the trenches are not necessarily made with two verticalside walls, but they could be made with other profiles, for exampleinclinable.

What is claimed is:
 1. Process for making an electrical connectionbetween two faces of a substrate comprising the following operations:the starting point is a conducting or semi conducting substrate, atleast one electrically insulating trench completely surrounding part ofthe substrate is made throughout the thickness of the substrate, thistrench being filled in over at least part of its depth, a firstconducting means is deposited on one of the faces of the substrate, thismeans being in electrical contact with the substrate over the partcompletely surrounded by the trench, this process comprising: a firstgroove is formed starting from a first face of the substrate, and thisfirst groove is filled in by at least one insulating material, thesubstrate is thinned until it has a desired thickness, a secondconducting means is formed on the thinning face of the thinned substratefacing the part of the substrate that is completely surrounded by thegroove, a second groove is formed starting from the thinning face of thethinned substrate, facing the first groove and opening up onto thematerial filling the first groove, said electrical connection thus beingset up by said part of the substrate completely surrounded by the trenchand by the first and second conducting means.
 2. Process according toclaim 1, in which a layer of electrically insulating material isdeposited on the walls of the first groove and this groove is filled inby another material.
 3. Process according to claim 1, in which thesecond groove is filled in.
 4. Process for making an electricalconnection between two faces of a substrate comprising the followingoperations: the starting point is a conducting or semi conductingsubstrate, at least one electrically insulating trench completelysurrounding part of the substrate is made throughout the thickness ofthe substrate, this trench being filled in over at least part of itsdepth, a first conductor is deposited on one of the faces of thesubstrate, this first conductor being in electrical contact with thesubstrate over the part completely surrounded by the trench, the processcomprising: forming a first groove, starting from a first face of thesubstrate, and filling in the first groove by at least one insulatingmaterial, thinning the substrate to a desired thickness, forming asecond conductor on the thinning face of the thinned substrate facingthe part of the substrate that is completely surrounded by the groove,forming a second groove, starting from the thinning face of the thinnedsubstrate, facing the first groove and opening up onto the materialfilling the first groove, said electrical connection thus being set upby said part of the substrate completely surrounded by the trench and bythe first and second conductors.
 5. Process according to claim 4, inwhich a layer of electrically insulating material is deposited on thewalls of the first groove and the first groove is filled in by anothermaterial.
 6. Process according to claim 4, in which the second groove isfilled in.
 7. Electrical connection between the two faces of aconducting or semi-conducting substrate, comprising: at least oneelectrically insulating trench extending throughout the thickness of thesubstrate and completely surrounding part of the substrate, this trenchbeing filled in over at least part of its depth, a first conductingmeans on one of the faces of the substrate, this means being inelectrical contact with the substrate in the part completely surroundedby the trench, a second conducting means on the other face of thesubstrate, in electrical contact with the substrate in said partcompletely surrounded by the trench, said connection thus being set upby the part of the substrate completely surrounded by the trench and bythe first and second conducting means, wherein the filled in part of thetrench comprises a first groove formed in the substrate starting from afirst face of the substrate, an electrically insulating material fillingin this first groove, and a second groove formed in the substratestarting from a second face of the substrate, this second groove havinga bottom opening up into the filled in part of the trench.
 8. Electricalconnection according to claim 7, in which an electrically insulatinglayer covers the wall of the first groove, and another material fills inthis first groove.
 9. Electrical connection according to claim 8, inwhich the material filling in the first groove has a coefficient ofexpansion similar to the coefficient of expansion of the substrate. 10.Electrical connection according to claim 7, in which the second grooveis also filled in.
 11. Electrical connection according to claim 8, inwhich the first conducting means is formed from a conducting track andthe second conducting means is an electrical contact pad.
 12. Electricalconnection between the two faces of a conducting or semi-conductingsubstrate, comprising: at least one electrically insulating trenchextending throughout the thickness of the substrate and completelysurrounding part of the substrate, the trench being filled in over atleast part of its depth, a first conductor on a first face of thesubstrate, in electrical contact with the substrate in the partcompletely surrounded by the trench, a second conductor on the otherface of the substrate, in electrical contact with the substrate in saidpart completely surrounded by the trench, said connection thus being setup by the part of the substrate completely surrounded by the trench andby the first and second conductors, wherein the filled in part of thetrench comprises a first groove formed in the substrate starting from afirst face of the substrate, an electrically insulating material fillingin the first groove, and a second groove formed in the substratestarting from a second face of the substrate, the second groove having abottom opening up into the filled in part of the trench.
 13. Electricalconnection according to claim 12, in which an electrically insulatinglayer covers the wall of the first groove, and another material fills inthe first groove.
 14. Electrical connection according to claim 13, inwhich the material filling in the first groove has a coefficient ofexpansion similar to a coefficient of expansion of the substrate. 15.Electrical connection according to claim 12, in which the second grooveis also filled in.
 16. Electrical connection according to claim 13, inwhich the first conductor is formed from a conducting track and thesecond conductor includes an electrical contact pad.